Solid state lighting arrays are used for a number of lighting applications. For example, lighting panels including arrays of solid state light emitting devices have been used as direct illumination sources in applications including architectural and/or accent lighting. A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs) or LED chips, which may include inorganic LED chips and/or organic LED chips (OLEDs). Typically, solid state light emitting devices generate light through the recombination of electronic carriers (electrons and holes) in a light emitting layer or region of a LED chip. LED chips have significantly longer lifetimes and typically have significantly greater luminous efficiency than conventional incandescent and fluorescent light sources; however, LED chips are narrow-band emitters, and it can be challenging to simultaneously provide good color rendering in combination with high luminous efficacy while maintain a maximizing brightness and efficiency.
Aspects relating to the subject matter disclosed herein may be better understood with reference to the 1931 CIE (Commission International de l'Eclairage) Chromaticity Diagram, which is well-known and readily available to those of ordinary skill in the art. The 1931 CIE Chromaticity Diagram maps out the human color perception in terms of two CIE parameters x and y. The spectral colors are distributed around the edge of the outlined space, which includes all of the hues perceived by the human eye. The boundary line represents maximum saturation for the spectral colors. The chromaticity coordinates (i.e., color points) that lie along the blackbody locus obey Planck's equation: E(λ)=A λ−5/(eB/T−1), where E is the emission intensity, λ is the emission wavelength, T the color temperature of the blackbody, and A and B are constants. Color coordinates that lie on or near the blackbody locus yield pleasing white light to a human observer. The 1931 CIE Diagram includes temperature listings along the blackbody locus (embodying a curved line emanating from the right corner). These temperature listings show the color path of a blackbody radiator that is caused to increase to such temperatures. As a heated object becomes incandescent, it first glows reddish, then yellowish, then white, and finally bluish. This occurs because the wavelength associated with the peak radiation of the blackbody radiator becomes progressively shorter with increased temperature, consistent with the Wien Displacement Law. Illuminants which produce light that is on or near the blackbody locus can thus be described in terms of their color temperature.
LED apparatuses typically receive a direct current (DC) input signal or a modulated square wave input signal so that a constant current flows through the LED chips when in an “on” state. A current value is typically set to provide high conversion efficiency. LED light sources with variable intensity may be controlled by changing duty factor of a modulated square wave input signal.
Conventional lighting systems for use in buildings are powered by an alternating current (AC) source; accordingly, a LED-based light source for use in buildings typically includes an AC-DC power converter. An AC-DC power converter often represents a significant fraction of the overall cost of a LED-based light source, and power losses inherent to such a power converter reduces overall efficiency of the light source. Additionally, AC-DC power converters are generally not as reliable as LED chips, and therefore can limit the operating lifetime of a LED light source.
To avoid disadvantages associated with use of AC-DC power converters, it has been proposed to operate a LED light source directly from an AC power source without AC-DC conversion. Multiple groups or sets of series-connected LED chips may be powered by different portions of an AC waveform. For instance, one group may be powered on when the amplitude of the AC waveform is positive, and another group may be powered on when the amplitude of the AC waveform is negative; however, this simple driving scheme typically suffers from flicker and reduced efficiency. To provide somewhat improved efficiency, a full-wave rectifier may be used; however, the resulting light source still has limited efficiency and may exhibit flicker.
Elimination of AC-DC power converters from solid state lighting apparatuses may enable enhanced cost and packaging efficiencies. It would be desirable to provide solid state lighting apparatuses with reduced volume (or size) and increased integration of functional components (e.g., including but not limited to driver components), in order to reduce production cost and provide lighting device designers with enhanced packaging flexibility, thereby promoting consumer adoption of solid state lighting devices. Achieving a high degree of functional component integration in lighting apparatuses may require placement of functional components proximate to solid state light emitter (e.g., LED) chips, thereby providing potential for such functional components to block, absorb, trap, or otherwise interfere with light emitted by one or more LED chips. It would be desirable to achieve a high degree of functional component integration in such solid state light emitting apparatuses while avoiding physical interference between light emissions and functional components in order to enhance light extraction and provide increased light intensity. Avoiding of such interference may enable reduction in the number of LED chips required per solid state lighting apparatus, thereby reducing heatsink requirements and reducing cost. Challenges persist in maximizing light extraction while reducing the number of LED chips required per solid state lighting apparatus.
Accordingly, a need exists for improved solid state lighting apparatuses and/or improved methods including use of solid state lighting apparatuses that can be directly coupled to an AC voltage signal, without requiring use of an on-board switched mode power supply. Desirable solid state lighting apparatuses and methods would exhibit improved light extraction, brightness, and/or improved thermal management. Desirable apparatuses and methods would also exhibit reduced cost and make it easier for end-users to justify switching to LED products from a return on investment or payback perspective.